This relates generally to displays, and more particularly, to displays with backlights.
Displays such as liquid crystal displays and other displays sometimes include backlight units. A backlight unit may include an array of light-emitting diodes and a backlight control integrated circuit (sometimes referred to as a backlight driver) that directly controls the array of light-emitting diodes. Displays with backlight units may be incorporated into an electronic device such as a computer or cellular telephone or may be implemented as stand-alone units.
The backlight driver may include a boost converter circuit and a current driver circuit. The boost converter circuit is controlled using a first clock signal exhibiting a first frequency to periodically provide a boosted voltage to the array of light-emitting diodes when the first clock signal is high. The current driver circuit is controlled using a second clock signal exhibiting a second frequency to periodically provide a source of current for the light-emitting diodes when the second clock signal is high. The first frequency associated with the first clock signal that controls the boost converter is typically substantially greater than the second frequency associated with the second clock signal that controls the current driver circuit. When the second clock signal is low, the current driver circuit is turned off, thereby preventing the array of light-emitting diodes from emitting any light.
In conventional backlight drivers, the first clock signal continues to toggle during both high clock phases and low clock phases of the second clock. In other words, the boost converter circuit is being continuously switched on and switched off even when the current driver circuit is turned off. Operating the backlight driver in this way consumes more power than necessary. Since the power consumption associated with switching on/off the boost converter circuit does not scale with the amount of current that is being delivered using the current driver circuit, power efficiency degradation is exacerbated at lower loads when the current driver is being used to deliver lower average current levels (i.e., when the backlight driver is being used to produce lower backlight levels).
It would therefore be desirable to be able to provide improved ways for operating the backlight driver to improve power efficiency.